Many electronic devices require a highly accurate time base for their operation. In particular, many electronic communication devices (e.g. radio transmitters or receivers for cellular telephones or other wireless communication devices) require a reference oscillator to provide a stable frequency source for proper operation. A reference oscillator typically uses a resonator circuit as part of its operation which drives the performance of the oscillator. Various types of resonators are used for oscillators include quartz crystals, surface acoustic wave (SAW) devices, LC circuits, silicon resonators, ceramics, film bulk acoustic resonators (FBARs), bulk acoustic wave (BAW) resonators, etc. In many devices, it is important to provide a reference oscillator which exhibits low phase noise and is highly accurate over variations in temperature, voltage, age, load, etc. to meet their performance specifications. In particular, some oscillators employ temperature compensation to maintain the frequency variation over the operating temperature range to within a few parts per million (ppm). W. D. Cowan, et al. “A 300-MHz Digitally Compensated SAW Oscillator,” IEEE TRANSACTION ON ULTRASONICS, FERROELECTRONICS, AND FREQUENCY CONTROL, May 1988 discloses one example of a self-calibrating temperature compensated crystal oscillator (SCTCXO).
However, prior reference oscillators can be improved upon in a number of ways for many applications. For example, for a cellular telephone or global positioning satellite (GPS) receiver, the component footprint on the printed circuit board is at a premium as further functionality continues to be integrated and the size and weight of the components continue to be reduced. Further size reduction, cost reduction, and performance improvements are areas where the current solutions are continually seeking advances.
What is needed, therefore, is a temperature compensated oscillator with an advantageous combination of size, cost, and performance characteristics.